Claude Code Found to Leave Steganographic Marks in Requests

Analysis of Anthropic's coding agent Claude Code (2.1.196) binary confirmed a steganography technique that hides data by making subtle changes to date strings within the system prompt.

This technique uses differences subtle enough that users or models wouldn't notice:

• Apostrophe ('s) changes: Depending on certain conditions, different Unicode characters such as ', ’, ʼ, ʼ are used.
• Date separator changes: For specific time zones (Asia/Shanghai, Asia/Urumqi), the date separator is changed from - to /.

These markers are determined based on the ANTHROPIC_BASE_URL environment variable value and the user's Timezone. The analysis found that the code contains logic to identify specific domains and keywords.

List of identification targets:

• Keywords: Major Chinese AI companies such as deepseek, moonshot, minimax, zhipu, baichuan, and others.
• Domains: baidu.com, bytedance.net, moonshot.ai, and various proxy/gateway domains.

This method could be used to conceal data by identifying the path (Proxy/Gateway) through which a request is routed or whether the user is from a specific region.